Non-metallic containers have achieved widespread commercial acceptance. These containers include a body made from plastic, paperboard, or a layered structure such as one or more layers of paperboard having interior and/or exterior polymeric film or foil layers. Typically these container bodies are easier to manufacture, are less expensive, and/or are more environmentally acceptable than prior metal containers.
In cylindrical form, non-metallic containers include a separate closure member at one or both ends of the cylinder. In some instances, the closure member may be a metallic closure member which is joined to the container body by outwardly rolling a portion of the lip of the container into a metallic flange of the metal closure, which is then crimped into the container body structure. Alternatively a peelable lidding member can be attached directly to a container body by means of a thermal seal formed between an integral lip on the container body and the lidding member.
For plastic container bodies, an integral top flange or lip can readily be formed during the molding process. However, for paperboard container bodies, the lip-forming procedure is typically accomplished in a step separate from formation of the body, per se.
For relatively thin walled container bodies, such as convolutely wound, frustoconically-shaped container bodies or container bodies formed of thin walled thermoplastic materials, it has been proposed to form a lip on the upper end by employing an apparatus including a splined surface support member, as disclosed in U.S. Pat. No. 4,680,016 to Lynch. The container body is forced onto the frustoconical splined support and the open end is then forced axially into a semicircular annual groove which initially forms an outwardly folded rim. Thereafter, a tucking finger, mounted at a rimming station, rolls the outward fold into a rolled lip as the mandrel supporting the container body is rotated.
For relatively thick walled paperboard container bodies, for example, having a wall thickness greater than about 0.015", e.g. from 0.020 to 0.055", rolled lips are more difficult to form. Conventionally, such rolled lips have been formed employing a metal can flanger of the type used to flange a metal can. This flanging apparatus has been used because of the high wall strength of thick walled paperboard container bodies. High wall strength is particularly apparent in spirally wound bodies formed of multiple layers of paperboard with and without inner and/or outer layers of film and/or foil materials. In addition to high wall strength, these spirally wound bodies have a true cylindrical shape and thus the walls of the open end are not flared outwardly adding to difficulty in forming a rolled lip.
The separate operation to form a rolled lip on relatively thick walled container bodies employing a separate flanging apparatus is both time consuming and requires added material handling procedures for passing partially formed container bodies to and from the flanging apparatus. Moreover, the use of the conventional flanging apparatus is a relatively slow process and the flanging apparatus is expensive.
To overcome this problem, an apparatus was proposed by the assignee of the present invention and is disclosed and described in assignee's U.S. Pat. No. 5,431,619 to Bacon et al. The apparatus of this patent includes a mandrel having a cylindrical-shaped portion and a lip forming annular cavity positioned coaxially with and axially spaced from the cylindrical portion of the mandrel. The annular cavity has a generally semi-circular cross-section formed by a single predetermined radius and includes an open mouth and a closed bottom extending outwardly of the mandrel. The mandrel additionally includes a frustoconically-shaped portion between the cylindrical portion and the lip-forming die. The frustoconically-shaped portion tapers radially outwardly in the direction toward the lip-forming die. An axial forcing means forces a cylindrical container body axially along the mandrel toward the lip-forming die to thereby stretch and outwardly flare the open end thereof as it passes over the frustoconically-shaped portion and the flared end is then forced into the cavity and along the semi-circular surface of the bottom portion and is rolled outwardly to form the lip.
This apparatus greatly improved the prior lip-forming operations for container bodies of the type discussed above; however, this apparatus can cause breakdown of the container body when the force exerted by the axial forcing means to force the container body into, along the surface of the die bottom portion, and through the lip-forming die exceeds the crush strength of the container body material.